The present invention relates to analog circuitry used to determine the ratio of two voltages raised to fractional powers.
Analog circuits that determine mathematical relationships find many uses in control systems used in manufacturing process control and feedback control of power processing equipment. In regulated power supplies, for example, the output voltage is compared to a reference to generate an error voltage proportional to the difference of these voltage levels. Sometimes the voltage levels of several outputs are summed to provide proportional control of all outputs. The error voltage is frequently integrated or differentiated to get improved transient response and loop stability. In other cases it may be necessary to raise error voltage to a fractional power to compensate for gain characteristics of another element in the feedback loop, or to divide the error voltage to a fractional power to compensate for gain variation due to input voltage or load current changes.
Simple mathematical functions are usually calculated with operational amplifiers and associated circuitry. Addition and subtraction can be achieved in a straightforward manner with the use of resistors, while integration and differentiation require capacitors or inductors. More complicated functions involving products or ratios are found by taking logarithms through use of the properties of a forward biased junction, adding or subtracting the result, and finally taking the antilogarithm.
Calculation of complex-expressions using operational amplifiers can require a very large number of components, adding substantially to the size and cost of the control circuit. In some instances simpler circuitry can be used to perform specialized calculations with reduced size and cost.
An object of the present invention is to provide a compact circuit that can provide the ratio of two voltages each raised to a preselected fractional power.
Another object of the present invention is to provide an output current which is representative of the ratio of two voltages each raised to a preselected fractional power.